Fabric tubes are well known for use as ducts to move air in large buildings, such as industrial plants and the like, as same can be more economical and quicker to install than metal ducts. Such fabric tubes are also commonly used in construction and similar temporary structure applications, as they are relatively light weight, economical, and easy to install, typically by hanger from the ceiling. Because of the light weight, the hangers do not need to be particularly strong, and can be fairly widely spaced.
Fabric tubes have also been commonly used as ducts to carry ventilation air long distances, such as in underground mines. Such tubes commonly include a hanger strip attached along a top of the tube with grommet holes defined therein to receive hangers attached to the ceiling of a mine passageway. As headroom in mine passageways may be limited, it is also known to provide fabric tubes with two side by side passageways to increase air flow capacity without increasing the diameter and further encroaching on available headroom. Such a double tube is disclosed for example in U.S. Pat. No. 5,094,273 to Eagleton.
Fabric tubes may be formed by welding or by sewing. While welding is generally more expensive and slower, welded seams are generally stronger than a sewn seam. With proper equipment, welded seam strengths can approach strengths recorded in the finished fabric. Ventilation engineers often qualify fabric tubes based on a pressure rating or the maximum working pressure of the air carried in the tube. The amount of ventilation air that can be moved through a tube is dependent on the pressure of the air generated by large diameter, high horsepower fans, with a higher pressure typically resulting in a higher volume of air moved and a reduction in electricity used. It is generally desirable to move as much air as possible in a given size tube, and so the pressure rating is an important factor when selecting a tube for a ventilation application. Welded seams are commonly used where higher air pressures will be used as there are no needle perforations for air leakage and in very high pressure applications, no potential for weakening and disintegration as the needle perforations expand from the pressure associated with the volume of air be pushed through the tube.
It is also known to fill a sealed fabric tube with water and position the filled tube as a flood control barrier as disclosed in U.S. Pat. No. 5,865,564 to Miller et al. The Miller tube is similar to a side by side double tube comprising a large tube with a divider flap welded across the middle that pulls the tube together as well as dividing it, and that results in an oblong cross section resting on a flat side that resists rolling in response to the pressure of flood waters being held at bay.